Field of the Invention
The invention relates to a capacitor assembly having an aluminum electrolytic capacitor which is installed in a casing that is closed by a cover disc, and two metallic connecting elements disposed in the cover disc for capacitor connections.
Such a capacitor assembly is known, for example, from the Siemens Matsushita Components Datenbuch 1997 "Aluminum Electrolytic Capacitors", pages 62-68.
There, the connecting elements have an internal thread, with conductors or busbars preferably being attached through the use of screws or threaded pins. In that case the connecting element on the anode side in the cover disc is composed of pure aluminum (Al 99.5 and purer), since it is wetted with electrolyte in the interior of the capacitor and a blocking oxide layer must be formed. The low strength of the soft, pure aluminum only permits low tightening torques when the electrical connections are attached, often leading to the thread being damaged during the fitting process. Furthermore, it is also quite common for connections to become loose again when stressed mechanically, resulting in poor contact.
In addition to the difficulties described above, the length tolerance of the components is a major problem when interconnecting a plurality of capacitors to form capacitor banks. On one hand, in order to dissipate the heat losses well, the base of the capacitor cup should be pressed firmly against the mounting plate. On the other hand, due to the increasing current load, the elements used for interconnection are becoming ever more solid and less flexible. That necessitates special length compensating elements, or interconnecting elements having a complex construction. The boards used for interconnection are generally seated on the upper level of the screw connections, which leads to increased inductance between the screw connections of the connecting elements.
Although it is possible to overcome the problem of low tightening strengths by using larger connecting threads, that in turn results in considerably greater costs for the cover disc. Length compensation through the use of compensating elements or through the use of more or less flexible connecting elements generally leads to unsatisfactory compromises with respect to heat dissipation and inductance, so that the structural configuration options for interconnection are highly constrained.